The present invention relates to a method and apparatus for plating a conductive material on a substrate. More particularly, the present invention is directed to a method and apparatus for depositing and altering the texture and electrical properties of the conductive material deposited on a semiconductor device, packaging substrate, or magnetic device/display.
A particular process step in the manufacturing of integrated circuits, devices, and packages involves plating a semiconductor wafer or workpiece (e.g., flat panel, magnetic recording heads, packages, etc.) surface with a conductive material. Plating the wafer or workpiece surface with the conductive material has important and broad application in the semiconductor industry.
FIG. 1 illustrates a cross sectional view of a substrate with topographical features having various layers disposed thereon. For example, this figure illustrates a substrate 2 with or without devices (i.e., transistors, etc.) having deposited thereon a barrier or adhesive layer 4 and a seed layer 6. The top surface of the substrate 2 may be patterned with vias, trenches, holes, and other features, or it may be flat. The barrier layer 4 may be tantalum (Ta), nitrides of tantalum (Ta), titanium (Ti), tungsten, TiW, CuWP, CoWP or combinations of any other material that is commonly used in this field. The barrier layer 4 is generally deposited on the substrate 2 by any of the various sputtering methods, by chemical vapor deposition (CVD), or by electrolyte/electroless plating methods. Thereafter, the seed layer 6 is deposited over the barrier layer 4.
The barrier layer 4 and the seed layer 6 may also be formed on the substrate 2 by using an electro-deposition method. This method offers distinct and unique advantages of lower costs and beneficial material properties (i.e., low stress in the substrate 2) as opposed to using other deposition methods.
The seed layer 6 material may be copper or copper substitutes. The seed layer 6 may be deposited on the barrier layer 4 using various sputtering methods, CVD, or electroless deposition or combinations thereof The seed layer 6 thickness, depending on the substrate 2 topography, may vary from 20 to 1500 xc3x85xc2x0, and may be discontinuous on the comers of the deep recesses of the substrate 2. After depositing the seed layer 6, a conductive layer 8 (e.g., copper layer) is generally electroplated over the seed layer 6 from a suitable acid or non-acidic plating bath or bath formulation.
In general, the texture of a large portion of the conductive layer 8 is dependent upon the texture of an underneath layer, for example, the seed layer 6. Texture as defined in this application includes, but are not limited to, the crystal orientation (i.e.,  less than 111 greater than ,  less than 110 greater than ), grain size, grain boundary (boundary around a single grain), etc. The texture of the remaining portion of the conductive layer 8 is dependent upon the chemicals in the plating bath and the deposition rate. In other words, if the crystal orientation of the seed layer 6 is formed predominantly in a  less than 111 greater than  orientation, then a large portion of the conductive layer 8 will have the same crystal orientation, that being  less than 111 greater than . With that being said, the texture of the seed layer 6 is also dependent upon the texture of the barrier layer 4.
When the plated conductive layer 8 is formed on the seed layer 6, the conductive layer 8 may be epitaxial with the seed layer 6 up to a thickness of about 3000 xc3x85xc2x0 from the top surface of the seed layer 6. However, when the thickness of the conductive layer 8 is above 3000 xc3x85xc2x0, the texture of the portion of the conductive layer 8 above 3000xc3x85xc2x0 may be dependent upon the nature of the plating bath.
After depositing the conductive layer 8, particularly when the conductive layer 8 is copper or gold, metallurgical grain recovery and grain growth generally occurs at room temperature. Thus, the grain size of the initially deposited conductive layer is typically about 30 to 100 xc3x85xc2x0, but can increase in size in the range of 2,000 to 10,000 xc3x85xc2x0 after grain growth at room temperature. The final grain size of the conductive layer 8 is dependent on the seed layer 6 material, the chemistry of the plating bath, and annealing temperature.
The texture of the annealed grains in the conductive layer 8 is often very similar to the texture of the grains of the seed layer 6. Thus, it is very difficult to form grains in the conductive layer 8 that are different in their texture from the grains of the seed layer 6. In addition, it is also difficult to accelerate room temperature grain growth of the conductive layer 8 without changing the texture of the seed layer 6, bath chemistry and/or temperature.
Accordingly, there is a need for a method and apparatus that can disassociate the texture of a plated conductive layer from that of the underneath seed layer. There is also a need for a method and apparatus that accelerates room temperature grain recovery and grain growth. Further, there is a need for a method and apparatus that can form a highly desirable conductive layer while increasing the grain size in the conductive layer.
It is an object of the present invention to provide a method and apparatus that plates a conductive material on a workpiece surface in a highly desirable manner.
It is another object of the present invention to provide a method and apparatus that plates a conductive material on a workpiece surface without an anode, pad type material, or other fixed feature making direct contact with the workpiece surface.
It is a further object of the present invention to provide a method and apparatus that plates a conductive material on a workpiece surface while a pad type material or other fixed feature is intermittently making contact with the workpiece surface.
It is yet another object of the present invention to provide a method and apparatus that plates a conductive material on a workpiece surface while a pad type material or other fixed feature is intermittently making contact with the workpiece surface in a xe2x80x9ccold workedxe2x80x9d manner.
It is a further object of the present invention to provide a method and apparatus that plates a conductive material on a workpiece surface in a manner such that a pad type material or other fixed feature makes contact with the deposited material with sufficient force to xe2x80x9ccold workxe2x80x9d the deposited material.
It is yet a further object of the present invention to provide a method and apparatus that electro-deposits a conductive material on a workpiece surface to form a symmetrical/nonsymmetrical composite plated layers consisting of xe2x80x9cnon cold worked layers/regionsxe2x80x9d and xe2x80x9ccold worked layers/regions.xe2x80x9d
In one preferred embodiment, the method according to the present invention includes the step of plating a conductive layer on the substrate using an anode/pad that rotates in a manner such that the plating solution is continuously applied onto the substrate without the anode/pad making contact with the substrate. Electrical power may be applied to the anode and the substrate during this plating process. After the conductive layer is formed on the substrate using the above stated method, the anode and the substrate may be momentarily de-energized, and the pad, which may or may not be rotating, is used to polish/rub against a top portion the conductive layer. Thus, the top portion of the conductive layer is polished during the xe2x80x9ccold workingxe2x80x9d process (e.g., when the anode and substrate are de-energized). This process can be repeated at least several times depending upon the type of the integrated circuit or device to be manufactured. In this manner, the texture of the conductive layer is altered such that a highly desirable conductive layer is formed.
In one embodiment of the present invention, the apparatus that performs such plating includes a circular platen having a pad type material attached thereto. The platen further includes a circular anode plate, where both the platen and the anode plate can rotate about a first axis while the workpiece may also rotate, move side to side, move in an orbital manner, or remain stationary. Upon application of power to the anode plate and the cathode workpiece, the plating solution can be flowed to or through the pad to plate the workpiece surface.
In another embodiment of the present invention, an apparatus that performs such plating includes a pad type material mounted on the cylindrical anode that rotates about a first axis. The metal from the plating solution can be deposited on the workpiece when a potential difference is applied between the workpiece and the anode.
In both embodiments, the pad may make intermittent contact with the workpiece surface after the conductive layer is formed on the substrate. The pad may smear, shear, polish/rub a top portion of the conductive layer in a xe2x80x9ccold workedxe2x80x9d manner such that the texture of the top portion of the conductive layer is altered.
Further, the present invention provides a method of forming an insitu cold worked layer with the deposited material during the deposition process, or alternate forming cold worked and non-cold worked layers on the substrate. The present invention also provides a method and apparatus for controlling the texture of the deposited conductive layer from the seed layer, bath chemistry, and temperature.
In addition, energy stored in the cold worked regions or portions of the deposited layer is used to accelerate the grain recovery and growth. Thus, large grain size can be obtained in the deposited material at a lower annealing temperature and a shorter annealing time.